DESCRIPTION:(Adapted from applicant's abstract): Stereotypy refers to behavior that is repetitive, rhythmical, topographically invariant, and without an obvious function. Although stereotypies can be observed in many species in different contexts, such behavior is typically associated, in humans, with various psychiatric, neurological, and developmental disorders, and, in animals, with adverse environmental circumstances. Although studies using pharmacological models of stereotyped behavior have identified important brain mechanisms, little is known about the neurobiological basis or function of spontaneous stereotypes in animals or humans. The investigators propose to study the development and neurobiological basis of abnormal stereotyped behavior in wild-type muroid rodents. A laboratory based rodent model offers significant advantages for these kinds of studies as much is known about the neurobiology of these species and large numbers of animals can be rapidly bred. The proposed studies will have three aims: To characterize the development of stereotyped behavior in deer mice; to prevent the development of abnormal stereotyped behavior by early environmental enrichment; and to identify important neurobiological mechanisms that mediate the development and expression of stereotyped behavior. Successful completion of the proposed studies will provide important information about the pathophysiology and treatment of stereotypic movement disorder in humans. Moreover, these studies will address basic brain mechanisms that mediate environmentally-induced stereotyped behavior, and the function of such behavior for the biological organism.